1. Field of the Invention
The present invention relates to a flow path exchanging valve which is a three-way valve or four-way valve and is used to exchange the flow path of refrigerant in a heat pump type air conditioner and more particularly, to a rotary flow-path exchanging valve for exchanging the flow path with the aid of the rotary operation of a valve element.
2. Description of the Prior Art
A previously known typical example of the rotary flow path exchanging valve is a four-way valve disclosed in J-UM-7-16084 (Laid-Open) which comprises a cylindrical valve housing, a valve element rotatably attached to the valve housing, a valve seat plate and an electromagnetic actuator. The valve seat plate includes a low pressure port secured to the valve housing and connected to a low-pressure conduit, a high pressure port secured to a high pressure conduit and at least one exchanging port.
The electromagnetic actuator includes a multi-polar magnet attached to the valve element and having N-poles and S-poles alternately arranged in a rotary direction of the valve element, an electromagnetic solenoid attached to the valve housing and a pair of magnetic poles which are magnetically connected to either one of an N-pole and S-pole generated by energizing the electromagnetic solenoid so that they are magnetized with the same pole as the one magnetic pole, and arranged at their positions out of phase by 180.degree. to oppose to either of the N-pole and S-pole of the multi-pole magnet.
The rotary flow-path exchanging valve is structured such that with the valve element in contact with the vale seat plate at its end surface, the magnetic force, generated in the magnetic pole piece of the valve housing, acts on the multi-pole magnet so that the valve element rotates to connect the exchanging port to either one of the low pressure port and high-pressure port selectively.
In the rotary flow-path exchanging valve, to complete the rotation of the valve element within the valve housing with no trouble is very important to make sure exchange of the flow path.
From this standpoint of view, it is important that the valve element is rotated smoothly when the electromagnetic solenoid is energized. Therefore, the weight of the valve element is very significant.
Meanwhile, the valve element itself, which is generally made of material of synthetic resin with high heat resistance, gives so large an increase in weight due to the material. The multi-pole magnet to be attached to the valve element greatly affects the weight of the entire valve element.
The valve element equipped with a multi-pole magnet in the conventional rotary flow-path exchanging valve is classified into two configurations, one in which the metallic multi-pole magnet formed by sintering is integrally attached by boding agent, ultrasonic fusing or mechanical bonding, and another in which the entire valve is formed of a plastic magnet.
Among them, the metallic multi-pole magnet formed by sintering, which has large weight, is not a preferable material to assure smooth rotation of the valve element. In addition, the metallic multi-pole magnet is not also preferable since it requires a metallic yoke separately to increase the weight of the entire rotary flow-path exchanging valve.
Further, in the configuration in which the metallic multi-pole magnet is integrally attached to the valve element, the end of the multi-pole magnet is apt to break because of its substance. Therefore, such a configuration is problematic in its strength, and is difficult to deal with.
On the other hand, the configuration in which the entire valve is formed of a plastic magnet does not give the problem of using the metallic multi-pole magnet since the former gives a smaller weight than the latter. But, in contrast, this configuration is difficult to give flexibility in hardness, and hence problematic in slidability. Because of this problem, it is uncertain to assure the smooth rotation of the valve element.
The molten resin of the plastic magnet, which is generally poor in flowablity, is poor in moldablity so that it is apt to give poorness such as sink or void. In addition, the configuration, in which the entire valve is formed of the plastic magnet, is difficult to set the plane degree of the sealing plane where the valve element is in slidable contact with the valve seat plate because of poorness of moldablity.
Therefore, in order to realize the light weight of the valve element with no trouble in rotation of the valve element when the multi-pole magnet is formed of the plastic magnet, the problem of slidability must be solved, and actually that of poor moldability and the attendant sealing property must be solved.
Accordingly, in order to realize the small weight of the valve element by using the multi-pole magnet formed of the plastic magnet, the above problems must be first solved. This completes the rotation of the valve element within the valve housing with no problem, thereby realizing sure exchange of the flow path.
In order to complete the rotation of the valve element within the valve housing with no problem in the rotary flow-path exchange valve, not only the above configuration of the multi-pole magnet, but also magnetic force on the multi-pole magnet must be continuously acted until the rotation of the valve element is completed. The magnetic force is generated in the magnetic piece of the valve housing when the electromagnetic solenoid is energized.
In the conventional rotary flow-path exchanging valve, as described above, the pair of magnetic pole pieces are arranged at their positions out of phase by 180.degree. to oppose to either one of the N-pole and S-pole of the multi-pole magnet. The are magnetically connected to one of the N-pole and S-pole generated when the electromagnetic solenoid is energized so that they are magnetized with the same polarity as that of the one magnetic pole. Such a configuration leads to the following problem.
When energization of the electromagnetic solenoid is stopped upon completion of exchange of the flow path, the magnetic force remaining in the pair of magnetic poles is weak. For this reason, if the magnetic force of the multi-pole magnet is strong, the magnetic force remaining in the pair of magnet pieces cannot attract the multi-pole magnet portion opposite to them when the valve element has been rotated.
Thus, the multi-pole magnet portion with an opposite magnetic polarity, adjacent to the multi-pole magnet portion opposite to the pair of magnetic pieces when the valve element has been rotated, approaches to attract each magnetic piece which is only metal with the magnetic polarity lost. Therefore, the valve element slightly rotates toward the opposite side to when the electromagnetic solenoid is energized so that the changing boundary of the magnetic poles in the multi-pole magnet is located at the center of the magnetic piece. Accordingly, the valve element cannot be held at a flow-path exchanging completing position.
However, if the magnetic force is reduced to suppress the reverse rotation of the valve element after the energization of the electromagnetic solenoid has been stopped, now the rotation torque generated in the valve element when the electromagnetic solenoid is energized is decreased. As a result, the valve element becomes apt to suffer from the influence such as friction and hence cannot be rotated surely.
In this way, in order that the magnetic force, generated in the magnetic piece of the valve housing when the electromagnetic solenoid is energized, is continuously acted on the multi-pole magnet until rotation of the valve element is completed, thereby completing the rotation of the valve element, the structure of the magnetic piece of the valve housing must be improved.
A rotary flow-path exchanging valve equipped with a pilot valve is proposed which includes a pressure chamber defined by the other end surface of a valve element within a valve housing and into which pressure at a high pressure port is introduced and the pilot valve for communicating the pressure chamber with a low pressure port. In this rotary flow-path exchanging valve, when an electromagnetic solenoid is energized, the valve element is rotated and the open/close of the pilot valve is also done.
In a stationary state, the rotary flow-path exchanging valve permits air-tightness between a high pressure port and a low pressure port in a stationary state. This is because the valve element is pressed on a valve seat plate owing to introduction of the pressure at the high pressure port into the pressure chamber. At the time of exchange of the flow path, the rotary flow-path exchanging valve opens the pilot valve prior to rotation of the valve element. Then, the high pressure state of the pressure chamber is released through communication of the pressure chamber with the low pressure port. Thus, the valve element floats from the valve seat plate by a difference between the pressure chamber and the valve seat plate, thereby rotating the valve element by low resistance.
In the rotary flow-path exchanging valve equipped with the pilot valve described above, the valve element is provided with a valve port which is opened/closed by the pilot valve to make connection/disconnection between the pressure chamber and the low pressure port. The pilot valve fits, movably in an axial direction, into a pilot guide formed in the valve housing and into a valve holding hole formed in the valve element. The pilot valve is individually supported by both valve housing having an electromagnetic solenoid and the valve element having the valve port.
Further, the high pressure port and low pressure port are arranged at a position displaced in a radial direction from the rotation center of the valve element on the valve seat. For this reason, when the valve element floats so as to be apart from the valve seat plate, the valve element tilts owing to the pressure of fluid flowing in between the valve element and valve seat plate from the high pressure port. As a result, rubbing occurs between the valve housing and pilot valve and between the valve element and pilot valve.
Thus, the movement of the valve element in a rotary axial direction and open/close operation of the pilot valve become unstable. This impairs smooth rotation of the valve element and simplicity of the operation of exchanging the flow path based on the rotation of the valve element. In addition, the main valve element and pilot valve suffer from abnormal aberration so that endurance thereof is impaired.